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Hardware Thread, Do I have to use the same hdd in RAID 5? in Technical; I have the TX300 S3 server with LSI MegaRAID SAS PCI Express(TM) ROMB (0) working with 5 hdd (ST3146854SS) in ...
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    Exclamation Do I have to use the same hdd in RAID 5?

    I have the TX300 S3 server with LSI MegaRAID SAS PCI Express(TM) ROMB (0) working with 5 hdd (ST3146854SS) in RAID 5. Two of the hard drivers are predicted to fail so I have to replace them ASAP. My question is . Do I have to use the same hdd as the manual says "(Replace the hard disk that is predicted to fail with a new one of the same model (with the same capacity and speed) as a rule."? I thought that you could use different hdds and the system will take the capacity/speed of the lowers. is that correct?. Need help please because if both of the hdd fail at the same time I will be in trouble. Thanks you very much in advance.

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    SYNACK's Avatar
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    Yes, it should work like this, I have done many expansions a drive at time upgrading one of set t a time to keep it live. As long as thy are bigger than the current ones you should be fine.

    As always take a backup first as good practice and for safety.

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    tmcd35's Avatar
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    The replacement drive should always be of the same capacity or larger than the other drives in the array. Brand/Manacturer/Model doesn't matter so much. The reason you are recommended to use the exact same model is to overcome the most common "gotcha". Two different drives of the same capacity, say 500Gb, may actually format to differing capacitys due to differences in technology used and manufacturers methods of describing drive space (500Gb Base10 =/= 500Gb Binary).

    While most of the time you'd probably be fine, you don't want the one drive that formats to 478Gb when all the others have formatted to 485Gb. For this reason, if I'm not using the exact same model then I tend to trade up a capacity, so buy a 620Gb drive and accept 120Gb of unused drive space.

    Not sure if I explained it very well, but that's my general understanding of using drives in RAID.

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    Thanks Synack.

    That’s what I though and I bought 2 new hdds (FUJITSU 300GB 15K PRIMERGY C-F-H-L-TX SAS HOTSWAP HD) but when I’ve read the manual ………. The think is I could try one (hotswap) and see if it works without issue for the system (in theory) but there is £188 in risk because if it won’t work I couldn’t return it.

    I've also sent an email to fujitsu so I will post here what they say.


    Thanks a lot.



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    Thanks tmcd35, very clear ;-)

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    Hi Alna1121

    Ideally you should try and keep the drives on brand and as close to original specification as possible to avoid any issues and additionally, LSI / Server vendor won't probably support you with a mixed brand array if you have an issue.

    I've seen issues in the past with mixed disks in arrays due to firmware revisions or changes in drive capabilities and ultimately the question you have to ask is - is saving a few pounds worth the hassle of diagnosing/fixing a disk issue.

    Key thing at the moment if you have suspect disks - make sure your backups are current !

    Let me know if you need any more help !

    Thanks,

    Ed

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    You are in very serious danger of a RAID failure with two drives predicted to fail on a RAID 5 array. With even one drive failure you are in danger of a RAID failure during rebuild as the likelihood of a URE occurring is relatively high. With two drives in a bad state there is a better than 50% chance you will not be able to successfully save the array.

    Your best course of action is to immediately take two full backups of all data on the array on two different physical backup devices, then to prevent any data being written to the array if at all possible while you attempt to perform the rebuild. You will want to use the same drives preferably (same firmware, size, etc.), but the most important thin is to save the data as your array is possibly, likely gone. If the rebuild fails, I strongly suggest you create a RAID 6 (good) or RAID 10 (better) array to replace it, then restore your data.

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    SYNACK's Avatar
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    Oh and something that no one else has said so far, if you are replacing two of the Five drives due to eminent failure then the others are probably getting close to popping off to, get another three and replace all of them that way you can also expand the capacity of the array while you're at it and call it an upgrade.
    Last edited by SYNACK; 13th March 2014 at 10:05 AM.

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    Michael's Avatar
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    As others have stated, so long as the capacity is the same or greater - but also (more crucially) specifications such as the rotational speed 5400rpm, 7200rpm should be the same, as well as the cache ideally.

    I've never tried, but I'm sure if you had hard disks of variable speeds, it would without doubt impact negatively on the RAID array.

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    I’ve forgotten to tell you something very important …. this is the master server so I think I am in real trouble. It looks like I must move the operations masters to the other server before change anything but this is 2003, the other is 2008. The global catalog is in other server as well so I think that if I am quick I will survive.

    Any thoughts will be very welcome


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    Thanks Michael,

    They are same manufacture, same speed but different cache, old 8mb (ST3146854SS) - new 16mb (ST3300657SS)

    Thanks

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    Quote Originally Posted by alna1121 View Post
    Thanks Michael,

    They are same manufacture, same speed but different cache, old 8mb (ST3146854SS) - new 16mb (ST3300657SS)

    Thanks
    You should just about get away with that. As for the roles, I'd advise transferring all roles before doing anything with the RAID array. Certainly easier rather than seizing roles from one to another.

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    Quote Originally Posted by Michael View Post
    You should just about get away with that. As for the roles, I'd advise transferring all roles before doing anything with the RAID array. Certainly easier rather than seizing roles from one to another.
    unless it goes wrong and you have to restore a backup that was pre role transfer id be tempted to leave them and sieze if i had to

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